BACKGROUND: coronary microvascular dysfunction may underlie the high cardiovascular risk associated with chronic kidney disease (CKD), but the effects of CKD on coronary microvasculature function remain uncertain.METHODS AND RESULTS: we assessed myocardial blood flow changes in mild-to-moderate CKD and analyzed the association between creatinine clearance (CrCl) and peak myocardial blood flow and coronary flow reserve (CFR) measured as the ratio of stress to rest perfusion at baseline and at 1 year in 435 nondiabetic individuals who underwent quantitative rest and pharmacological stress positron emission tomography imaging. At baseline, CFR was significantly associated with CrCl (β per 10 mL/min increase, 0.07; P=0.001). Factors such as age and blood pressure accounted for this association, and it was not significant in adjusted analyses (β=-0.02, P=0.53). Peak flow was not associated with CrCl in either crude or adjusted analyses (β per 10 mL/min=-0.02 mL/min per g, P=0.29). Although change in peak flow at 1 year was similar in patients with and without CKD, CrCl was a strong and independent predictor of a higher rate of change in CFR, with a loss of 0.11 CFR units/y (95% confidence interval, 0.01 to 0.20) for each 10 mL/min drop in CrCl (P=0.03).CONCLUSIONS: these findings demonstrate that mild-to-moderate CKD is not independently associated with a reduction in peak myocardial flow or CFR and suggests that microvascular changes are unlikely to explain the high cardiovascular mortality in mild to moderate CKD. Loss of CFR, however, may accelerate in mild to moderate CKD. Further studies are needed to determine whether these changes lead to more significant reductions that may reduce peak flows and CFR and contribute to cardiovascular risk in more severe CKD.